Colosseum

Each world features its own dedicated colosseum. The tickets required for entry are the same for all colosseums, but the monsters you encounter and the rewards you earn are unique to each world.

All colosseums feature the same basic mechanics:

You have 5 minutes to complete the colosseum. Whether you clear all waves or run out of time, you'll receive reward chests at the end based on your final score.
There are 15 waves of monsters. The final wave includes a boss. All 15 waves + the boss must be cleared in order to earn Golden Chest rewards.
Pressing 'Next Round' will progress to the next round immediately, and increase your score multiplier. However, the more enemies there are on the screen, the faster your multiplier will decrease! You must defeat them quickly to maintain your score multiplier.
Getting multi-kill combos also contributes to your score multiplier.
Clearing the full colosseum with time remaining will earn you a Time Bonus, increasing your score.

Colosseum Tips

Spears are the weapon of choice early on, as they hit multiple monsters at once, and colosseum monsters spawn very close to one another - this helps you earn multi-kill combos and finish under the time limit. The only Spear non-Warriors can equip is the Wooden Spear.
Use your active attacks (the ones you equip to your attack bar) strategically to take out waves. Turning off auto or turning off the "Use attacks in auto" option will ensure the AI doesn't waste your strongest moves.
If your damage and strategy are solid, increasing your Movespeed can help you finish within the time limit/set new high scores. If you don't need healing food/damage food, swap in Speed Potions.
If you die in the colosseum and don't have an Insta-Rez remaining, your Town Respawn will let you collect your rewards.